1. Field of the Invention
The present invention relates to a photoelectric conversion apparatus, and more particularly, to a photoelectric conversion apparatus for use to achieve auto focusing based on phase difference detection.
2. Description of the Related Art
In general, characteristics to be considered in designing of the photoelectric conversion apparatus include a high signal-to-noise ratio, a large dynamic range in terms of the amount of incident light, etc. Japanese Patent Laid-Open No. 9-046596 discloses a photoelectric conversion apparatus in which a floating diffusion (FD) element is used to detect the amount of an electric charge accumulated in a photodiode. In the technique disclosed in Japanese Patent Laid-Open No. 9-046596, the detection capacitance is reduced by using the photodiode in a depleted state thereby improving the signal-to-noise ratio. Furthermore, one FD element is shared by a plurality of photodiodes to allow the photodiodes to have a large light receiving area. This allows it to generate a large amount of electric charge even when the amount of incident light is small, and thus an increase in the signal-to-noise ratio can be achieved for low luminance. Japanese Patent Laid-Open No. 2006-165754 discloses a technique to change a charge-to-voltage conversion factor by adding capacitance to the FD element thereby achieving an expansion of the dynamic range.
In the technique disclosed in Japanese Patent Laid-Open No. 9-046596, although sensitivity in a low luminance condition can be increased, it is difficult to expand the dynamic range in a high luminance condition. In the technique disclosed in Japanese Patent Laid-Open No. 2006-165754, the addition of capacitance makes it difficult to achieve an increase in sensitivity in the low luminance condition. That is, it is difficult to simultaneously achieve both an increase in sensitivity and an increase in dynamic range.